title: Fabrication of hollow metal oxide nanocrystals by etching cuprous oxide with metal(II) ions: approach to the essential driving force.
abstract: Hollow metal oxide nanocrystals were prepared by etching cuprous oxide with metal ions and were applied as photoelectrodes. As a hard template, polyvinylpyrrolidone stabilized cuprous oxide (PVP-Cu2O) and non-stabilized cuprous oxide (nPVP-Cu2O) were synthesized by a precipitation method. Hollow iron oxide and cobalt oxide nanocrystals with a truncated octahedral morphology were fabricated by an etching reaction with transition metal(II) ions (Fe(2+) or Co(2+)). In the etching reaction process, a cationic exchange reaction occurs between the divalent metal ion and Cu(+) due to the higher Lewis acidity. Facet selective etching of cuprous oxide has been observed during the ionic exchange reaction of Cu(+) and O(2-) ions in PVP-Cu2O complexes with transition metal(II) ions (Fe(2+) or Co(2+)) at the surface of a (110) facet. Amorphous states of hollow metal oxide products were annealed to form α-Fe2O3 (hematite) and Co3O4 and their crystal structure was examined with X-ray diffraction and HR-TEM. The optical absorption behavior of semiconductor nanocrystals was measured with UV-vis spectroscopy to define band gap energy. The hollow hematite structure has a 2.08 eV band gap and Co3O4 (Co(II,III) oxide) has a 1.80 eV indirect band gap. Using these hollow nanocrystals, a metal oxide monolayer film was fabricated with a secondary growth approach and was studied for its photocatalytic properties.
authors.affiliation: Korea Center for Artificial Photosynthesis, Department of Chemistry, Sogang University, Seoul, 121-742, Republic of Korea. yskang@sogang.ac.kr.
authors.forename: Jong Hwa
authors.initials: JH
authors.lastname: Sohn
authors.forename: Hyun Gil
authors.initials: HG
authors.lastname: Cha
authors.forename: Chang Woo
authors.initials: CW
authors.lastname: Kim
authors.forename: Do Kyoung
authors.initials: DK
authors.lastname: Kim
authors.forename: Young Soo
authors.initials: YS
authors.lastname: Kang